The 2001 Survey of Children with Special Health Care Needs (CSHCN) shows that, among children less than 3 years of age, the prevalence of health and developmental impairments significant enough to warrant increased medical or therapeutic services or to impact daily living is 6.5% (Data Resource Center, CSHCN). However, this data underestimates children at risk for developmental difficulties. In a similar nationally representative survey, the National Survey of Children's Health, 40% of parents of children less than 5 reported concern that their child was at risk for neurodevelopmental difficulties including delayed language acquisition, poor social skills, and limited mobility (The Health and Well-Being of Children: A Portrait of States and the Nation, 2005). Early childhood social policy, the Individuals with Disabilities Education Act Part C, was promulgated to create state Early Intervention (EI) programs in order to ameliorate neurodevelopmental risk among infants and toddlers. Qualitative studies reveal that there exists extreme variation across states in many facets of Part C programming including eligibility requirements (Spiker, 2001), models of service coordination (Scarborough, 2004) while quantitative studies suggest mixed effect of EI in small samples (Shonkoff, 1986; Hebbeler, 2007). What is unknown are the social determinants of variability of EI participation, the degree to which health and developmental services are coordinated and seamless, and whether EI is associated with improved neurodevelopmental outcomes at the population level. The purpose of this research is to examine, among a cohort of young children at risk for neurodevelopmental difficulties, 1) the social determinants in participation In Early Intervention services and the extent to which these might be explained by relevant sociopolitical, contextual factors (Paper 1), 2) the social determinants in satisfaction with care coordination and the extent to which these might be explained by relevant sociopolitical, contextual factors (Paper 2), and 3) the relationship between changes in neurodevelopment over time and participation in Early Intervention (Paper 3). This research will be completed to fulfill my doctoral dissertation requirement of three publishable quality manuscripts. It will entail secondary data analyses using two nationally representative surveys, the 2005 National Survey of Children with Special Healthcare Needs and the Early Childhood Longitudinal Study Birth Cohort. For the first two papers, multi-level modeling will be used, which allows for investigation of individual and contextual level variables simultaneously while appropriately addressing the clustering of individuals within states. The third paper will entail a longitudinal analysis which will allow for an investigation of the relationship between EI participation and neurodevelopmental outcomes over time. This research will contribute to the field of public health as it directly relates to not only social policy and programmatic initiatives aimed at addressing social disparities in access to health and developmental services for vulnerable populations, but also is consonant with the CDC's objective of promoting "Healthy People at Every Stage of Life." Early Intervention (EI) is a federally mandated, state-based program to reduce developmental risk in infants and toddlers. This study will explore social determinants of access to, satisfaction with, and effectiveness of EI programming among a nationally representative sample of children at risk for developmental difficulties. [unreadable] [unreadable] [unreadable] [unreadable]